The present invention relates to a multicolor image-forming material and, in more detail, it relates to a photosensitive transfer sheet to be used primarily for obtaining a prepress color proof usable for the proofreading operation indispensable in the photo-engraving process.
In the color printing, the prepress color proof is made for checking the finished color, tone, etc. of print mainly by overlay method or surprint method so far, depending on the shape thereof.
In the overlay method, each color-decomposed original plate is printed on a transparent supporter coated with colored sensitizer for every color and each color is superposed on a white sheet to perform the proofreading (U.S. Pat. No. 3136637, U.S. Pat. No. 3221553 and U.S. Pat. No. 3326682). This method allows rapid proof-making and can be utilized for preparing a color-separated proof by properly combining two or three colors. With this type, however, each transparent supporter is superposed, thus turbidity generates and remarkable difference occurs sensually compared with the print printed on a press or proofing machine.
As for the method to form a multicolor image by surprint system, various methods have been proposed. Thereamong, in a method of using pressure-sensitive adhesive, colored photosensitive layer and pressure-sensitive adhesive layer are layered in this order on a supporter and, after closely and sufficiently contacted the surface of adhesive layer with a white base paper mount to be transferred under pressure, the supporter is peeled off, thereby transferring the colored photosensitive layer onto the paper mount. Then, a color-decomposed manuscript corresponding to the color tone of said colored photosensitive layer is closely contacted and exposed to light, and the colored photosensitive layer is developed with exclusive developing solution and dried to make a decomposed image. Same procedure is repeated thereon further with remaining colors to form a multi-color image (Japanese Patent Publication No. Sho 47-27441).
Moreover, with respect to a method of transferring by heat without using pressure-sensitive adhesive, there are various proposals. These include, for example, a method wherein the manuscript is superposed and contacted closely with a material provided with colored photopolymerizable layer exhibiting adhesiveness at a temperature higher than certain temperature on a supporter and exposed to light, and only the nonexposed area is transferred onto a paper base because of the exposed area becoming to exhibit no adhesiveness (U.S. Pat. No. 3203805), a method wherein, after the colored polymerisable layer was exposed to light and developed, the colored image is transferred under heat onto a base having thermosensitive adhesive (U.S. Pat. No. 4304836), a method wherein, after a material consisting of supporter/release layer/colored photosensitive layer was exposed to light and developed to obtain a colored image, the thermosensitive adhesive is coated onto the surface receiving said adhesive or image to transfer under heat (U.S. Pat. No. 3721557, Japanese Patent Publication No. Sho 46-15326 and No. Sho 49-441), or the like.
So far, for the colored photosensitive layer (negative type) to be used for such purpose, various types have been proposed, but combinations of film-forming water-soluble high-molecular substance, photo-insolubilizing agent and coloring agent are used widely in general. As the film-forming water-soluble high-molecular substances, a lot of substances, e.g. poly(vinyl alcohol), gelatin, casein, glue, alginic acids, gums, cellulose derivatives such as carboxy-methylcellulose and hydroxymethylcellulose, polyacrylic acid and its salts, polymethacrylic acid and its salts, polyacrylamide, poly(ethylene oxide), poly(vinyl pyrrolidone), etc. can be mentioned. Also, the photo-insolubilizing agents include diazonium salts, their condensates, tetrazonium salts, bichromates, azide compounds, etc., thus many combinations are used.
With these combinations, however, under the influences that diazonium salts, their condensates, tetrazonium salts, etc. being the photo-insolubilizing agents are colored and, in addition, the photo-decomposed residues after exposure to light are colored, there have been drawbacks that the coloring agent used is contaminated making it difficult to obtain pure color tone of coloring agent and the feeling of transparency lacks. Further, it was needed to sufficiently take a care for the handling in all cases because of the fogging on preserving at high temperature and high humidity.
Moreover, previously, in Japanese Unexamined Patent Publication No. Sho 61-186955 and No. Sho 61-286858, a method of forming multicolor image and a material therefor applicable also to the color proof were found, which had a number of superiorities such that, since all the treatments could be carried out in a light room and the development treatment could also be performed only with water, they were advantageous in the aspects of environment and safety such as explosion and that they were excellent in the operativity and not only the material cost but also running cost could be saved drastically.
Namely, this is a method of forming a multicolor image characterized in that a heat-transferable photosensitive sheet provided with a colored photosensitive layer being water-soluble and insolubilized by light, of which photosensitive agent being represented by a general formula (I) or (II), ##STR2## (wherein R.sub.1 and R.sub.2 denote hydrogen atoms or alkyl groups independently one another, Y.sup.- denotes a conjugated chlorinic ion of acid, m denotes an integer of 1 to 6, and n denotes 0 or 1), via a heat-fusible and-bondable intermediate layer on a transparent supporter is treated through the steps comprising:
(1) a step wherein said photosensitive material is contacted closely with a negative manuscript and exposed to actinic rays therethrough, and then the nonexposed area is dissolved out by washing with water to form an image, and
(2) a step wherein the surface of said formed image is further contacted closely with the heat-fusible and -bondable surface of an image-receiving material having a heat-fusible and -bondable layer and pressurized under heat, and then the transparent supporter is peeled off from the intermediate layer having the heat-fusibility and -bondability to transfer the colored image onto the image-receiving material together with the intermediate layer, thus, first, photosensitive materials with colored photosensitive layer different in the color tones are prepared, negative manuscripts are selected corresponding to each color tone, they are contacted closely and exposed to light, and the colored photosensitive layers are washed with water to dissolve out nonexposed area to form images in the step (1), and, next, the colored image with a particular color tone thereamong is transferred onto the image-receiving material in the step (2), then
(3) a step wherein the image surface of photosensitive material with a colored image different in the color tone from above is further contacted closely with the heat-fusible and -bondable surface of image-receiving material having finished the transfer obtained in the step (2) and pressurized under heat, and then the transparent supporter is peeled off from the intermediate layer to transfer the colored image onto the already transferred surface of image-receiving material together with the intermediate layer and, for the third and subsequent colors, the step (3) is repeated.
This method can give a prepress color proof being excellent in the preservability, allowable the development treatment only with water in addition to the handling in a light room, further, uncontaminative in the color tone of coloring agent used, and possible to finish very closely to the print or proof.
However, in this method, too, there was a problem in the registering accuracy for obtaining a prepress color proof with higher precision. That is, the problem lies in that, since the images with different color tones obtained previously by exposing the photosensitive materials to light and developing them are contacted one by one with the heat-fusible and -bondable surface of image-receiving material and they are transferred by the pressurizing treatment under heat, the registering is very difficult, leading to a poor accuracy of register.
The purpose of the invention is to provide a multicolor image-forming material usable for the high-precision prepress color proof with a finish very close to the print by surprint method, and, in more detail, to provide a multicolor image-forming material for obtaining the high-precision prepress color proof being excellent in the preservability, allowable the development treatment only with water in addition to the handing in a light room, further, uncontaminative in the color tone of coloring agent used, turbidity-free and excellent in the registering accuracy.